BSCI 424 Pathogenic Microbiology - Host-Pathogen Interactions

Vocabulary flashcards generated from the BSCI 424 Pathogenic Microbiology lecture, detailing host-pathogen interactions, normal microflora, host defense mechanisms, adherence structures, biofilms, and intracellular invasion pathways.

Endogenous Pathogens

Opportunistic microorganisms that are part of the host's normal microflora but cause disease when host defenses are weakened or when translocated to normally sterile body sites.

Exogenous Pathogens

Classical disease-causing microorganisms originating outside the host body that enter to establish an infection.

Mucociliary Escalator

A secondary physical defense mechanism of the respiratory tract where cilia move mucus and entrapped foreign particles upward away from the lungs.

Cell Shedding

A physical host defense mechanism in epithelial tissues where surface enterocytes undergo apoptosis and slough off along with adherent bacteria.

Antibacterial Peptides

Conserved molecules $10-40$ amino acids in length that insert into bacterial membranes to induce lethal pore formation while leaving host eukaryotic membranes protected by cholesterol.

Non-Shedding Surfaces

Anatomical or artificial structures in the human body that do not shed surface cells—such as tooth surfaces and prosthetic devices—making them key sites for biofilm development.

Fecal Microbiota Transplantation (FMT)

A procedure first performed in 1958 to restore healthy gut microflora, shown in a 2013 trial to yield an $80\%$ positive response compared to $30\%$ for vancomycin in treating recurrent Clostridium difficile infections.

Pathogen-Associated Molecular Patterns (PAMPs)

Conserved microbial molecular structures (such as LPS) recognized by host cell Pathogen-Recognition Receptors (PRRs) like Toll-like receptors to activate innate immune responses.

Bacterial Capsule

A highly hydrated polysaccharide or polypeptide layer loosely associated with the cell exterior that acts as a major virulence factor for mucosal adherence and host immune evasion.

Electrostatic Repulsion in Adhesion

The repulsive force occurring at a separation distance of $10-20\,\text{nm}$ between net negatively charged bacterial and host cell surfaces, which elongated structures like pili and flagella help overcome.

Biofilm

A complex microbial community attached to non-shedding surfaces that exhibits increased resistance to antibiotics and host defenses, associated with diseases like periodontitis and endocarditis.

Zipper Mechanism

A cellular invasion mechanism where a bacterium (such as Listeria or Yersinia) induces localized host actin organization, causing the bacterium to sink directly into the non-phagocytic cell without forming large membrane ruffles.

Trigger Mechanism

A cellular invasion mechanism where a bacterium (such as Shigella or Salmonella) triggers extensive host actin polymerization, pushing plasma membrane sheets out to engulf the bacterium via macropinocytosis.

Bacterial Cell Structure

Anatomical features of a bacterial cell, including external structures (flagellum, capsule, fibrils/fimbriae, S layer) and internal components (cell wall, cytoplasmic membrane, periplasmic space, nucleoid, inclusion body).

Phases of Biofilm Formation

The multi-step sequence of biofilm development over a substratum, progressing through initial Adhesion (planktonic cells becoming adherent on a conditioning film), Colonisation (matrix formation), and Growth.

Bacterial Induced Actin Rearrangements

Pathogenic interactions manipulating host cell actin cytoskeleton, categorized into intracellular Invasion mechanisms (Zipper vs. Trigger) and extracellular effects (Prevention of phagocytosis in Yersinia and Pedestal formation in EPEC).